Business, science and entertainment applications depend upon computing systems to process and record data. In these applications, large volumes of data are often stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical, convenient, and secure means of storing or archiving data.
Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is currently measured in hundreds of gigabytes.
FIG. 1 illustrates a traditional flat-lapped bi-directional, two-module magnetic tape head 100, in accordance with the prior art. As shown, the head includes a pair of bases 102, each equipped with a module 104. The bases are typically ceramic beams shaped in the form of a U that are adhesively coupled together. Each module 104 includes a substrate 104A and a closure 104B with readers and/or writers 106 situated therebetween. In use, a tape 108 is moved over the modules 104 along a tape bearing surface 109 in the manner shown for reading and writing data on the tape 108 using the readers and writers 106. Conventionally, a partial vacuum is formed between the tape 108 and the tape bearing surface 109 for maintaining the tape 108 in close proximity with the readers and writers 106.
Two common parameters are associated with heads of such design. One parameter includes the tape wrap angles αi, αo, defined between the tape 108 and a plane 111 in which the upper surface of the tape bearing surface 109 resides. It should be noted that the tape wrap angles αi, αo includes an inner wrap angle αi which is often similar in degree to an external, or outer, wrap angle αo. The tape hearing surfaces 109 of the modules 104 are set at a predetermined angle from each other such that the desired inner wrap angle αi is achieved at the facing edges. The wrap angles αi, αo, and tape bearing surface length 112 are often adjusted to deal with various operational aspects of heads such as that of FIG. 1.
The external wrap angles αo are typically set in the drive, such as by adjustable eccentric-axle rollers. The offset axis creates an orbital arc of rotation, allowing precise alignment of the wrap angle αo. However, situations arise where rollers may not be the most desirable choice to set the external wrap angles αo. For example, rollers require extra headroom in a drive, particularly where they are adjustable. Additionally, rollers, and particularly adjustable roller systems, may be more expensive to install in the drive. A further drawback of this approach is mechanical alignment cannot be completed independent of signal read readiness.
FIG. 2 illustrates one proposed solution to set the desired external wrap angles αo, and which may be less expensive than implementing adjustable rollers. The proposed solution comprises forming outriggers 150 on the module 104, as shown in FIG. 2. The outriggers 150 set the external wrap angles αo. However, as the fabrication of tape head components moves towards use of thinner wafers, the distance between the front and back faces of the module 104 is reduced. When outriggers 150 are used, a minimum free space span between the outrigger inner edge 152 and the outer edge 154 of the primary tape bearing surface 109 is required so as not to disrupt the aforementioned tape effects, namely tenting. Particularly, in a flat-profile tape head (as shown), the elements 106 are positioned between the substrate 104A and a closure 104B. The primary tape bearing surface 109 needs to be long enough in the direction of tape travel so that tenting does not occur over the elements 106, because reliability of the read/write functions depends in part on the tape-head spacing.
One problem associated with the systems described above is that they are susceptible to sporadic tape lateral motion jumps. These motion jumps are believed to be caused by lateral shifts of the tape as it wraps around the spool in the tape cartridge. Air between the tape wraps effectively acts as a lubricant, which allows the tape to shift laterally one way or the other as it is wrapping onto a reel.
The back coat of the tape is intentionally not as smooth as the front coat to help the tape roll up on the reel without excess air build up between wraps on the reel. The rougher back coat allows the air to bleed out between the surface features as well as enhances friction between the rolls of tape on the reel. However, some air may remain, allowing the tape to shift as it rolls onto the spool.
These shifts create problems when the tape is despooling, namely that the angle of approach of the tape as it enters the guide system changes. The resultant lateral motion of the tape causes tape shift and skew, which in turn can cause misregistration between head and tape. For instance, as the tape unwraps, any lateral shifting in the tape wrap translates through the guide assembly and causes a corresponding motion jump of the tape relative to the head that the actuator may not perfectly track.
Tape lateral motion hops also put a lower bound on stop write thresholds, and so ultimately on track density. The only known solution to this problem is to have the head inserted between the tape and a large roller guide. This has the drawback that there is very little space to fit the head, cables and actuator. The compromises add complexity and cost to head design and build. A solution is needed that has the same advantages, but removes the space restrictions.